tvhlog: move output to a thread

I'm hoping this will give a small performance boost with heavy levels
of trace. This is because I'm finding that data appears to be missing
when testing EIT, but to test I need to enable debug and I think that
debug may be part of the problem!
mpegts: fix debug display bug and event firing
mpegts: add the concept of a mux level subscription

This is necessary so that things like EPG grabbing can make
subscriptions that take precedence over initial scan but not
over standard subscriptions.

Will also be used for the debug mux dump from UI feature.
mpegts: allow out of sequence table processing

also corrected invalid length check and added lots of extra debug
linuxdvb: ensure that PID filters are not installed early

I thought this was causing stale data to enter the pipelines, turns
out this was not the case (it was just a NIT entry for a mux that
didn't exist colliding with one that did).

However still a useful mod.
epggrab: complete update to OTA mux and EIT

Still haven't touched OpenTV and there are several hacks in here for which
a proper solution is required.